In a turbomachine of which the final stage of the compressor is of the centrifugal type, a diffuser-distributor assembly is arranged at the outlet of the centrifugal stage and supplies an annular combustion chamber with air.
The diffuser comprises an annular downstream end-piece that is connected at its downstream end to means for injecting air into a circuit for ventilating a turbine situated downstream of the combustion chamber. A portion of the airflow coming out of the distributor flows round the combustion chamber via the inside, while passing between a radially internal wall of the chamber and the end-piece of the diffuser, to supply these air injection means for ventilating the turbine.
An annular cavity is delimited downstream of the impeller of the centrifugal stage by the annular end-piece of the diffuser and must be ventilated, by taking air from the outlet of the centrifugal stage, in order to prevent an increase in temperature of the downstream face of the impeller that would be likely to exceed the maximum temperature admissible by the material of the impeller, the air present in the cavity being driven by the impeller and heated by viscous friction.